The present invention relates to the general field of balancing a turbine engine rotor, and in particular a fan of an airplane turbojet.
In known manner, a turbojet has a fan feeding air to a primary flow channel including in particular a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, and a low-pressure turbine.
At its upstream end, the turbojet has an air inlet for feeding the fan. This inlet comprises in particular a disk having blades mounted thereon that are circumferentially spaced apart from one another. An inlet cone is fastened on the fan disk in order to deflect the air admitted into the turbojet towards the fan blades.
In order to compensate any unbalance that might affect the rotating fan while the turbojet is in operation, and thus in order to reduce engine vibration, it is known to balance the fan by using screws that form balance weights that are engaged in the disk or in the inlet cone. More precisely, these screws are of mutually different lengths so as to give them different weights. The number, the positions around the axis of rotation of the fan, and the lengths of these screws define a balancing configuration for the fan on which they are installed.
Likewise, in order to compensate the unbalance affecting the low-pressure turbine in rotation during operation of the turbojet, clips are mounted on the free ends of the blades of the last stage of this turbine. The numbers and the positions of these clips define a balancing configuration of the low-pressure turbine, which is installed thereon.
When calculating a new balancing solution, it is important for the balancing configurations for the fan and for the low-pressure turbine that have actually been installed to be known. For this purpose, the balancing configurations are stored in the electronic computer of the engine (also known as an engine monitoring unit (EMU)). Calculating a new balancing configuration thus implies that the EMU has stored in its memory the configurations of the screws installed on the fan and of the clips mounted on the last stage of the low-pressure turbine. Unfortunately, in the event of the EMU being replaced, the balancing programs stored in memory are lost and it is necessary to reinitialize the memory of the new EMU with the configurations of the screws actually installed on the fan and of the clips mounted on the last stage of the low-pressure turbine.
In order to discover the configuration of these screws installed on the fan, it is therefore necessary to unscrew each screw, to observe its length in order to know its weight, and then to screw it back on. Likewise, in order to discover the configuration of the clips mounted on the blades of the last stage of the low-pressure turbine, it is necessary either to partially dismantle the rear end of the engine, or else to use a special tool for accessing this stage together with appropriate viewing means. These inspection operations are laborious and they require qualifications that the technician in charge of reinitializing the memory of the EMU need not necessarily possess.
In order to mitigate such drawbacks, French patent application No. 12/61830 filed on Dec. 10, 2012 by the Applicant proposes that each screw forming a balance weight presents a screw head with a particular visual characteristic that is associated with its weight (e.g. a particular shape or color) and that can be detected directly by the naked eye (the screw heads do not all match). Thus, during an operation of reinitializing the memory of the EMU of the engine, the balance weights that are mounted on the rotor, e.g. on the fan of the turbine engine, are identified merely by looking at the screw heads and comparing their characteristics with a pre-established table.
Nevertheless, with such a solution, human errors are possible while identifying the various visual characteristics of the screw heads and their angular positions on the rotor, so there a risk that the balancing configuration installed on the rotor is not correctly identified.